How to pull unrelated data in a column from two tables.? - sql

Question

I have following two tables:
BenPlan
BenPlanId BenPlanName BenPlanRate EmployeeCost
-----------------------------------------------------
1 Medical 0.45 5000
2 Dental 0.75 2000
EmployeeBenPlan
EmployeeId BenPlanId EffectiveStart EffectiveEnd
-------------------------------------------------------
1 1 1/1/2019 NULL
2 2 1/1/2019 NULL
Now, I have to make a report which shows data as under:
EmployeeBenPlanDetails
EmployeeId BenPlanName Rate EmployeeCost EffectiveStart EffectiveEnd
--------------------------------------------------------------------------------
1 Medical 0.75 5000 1/1/2019 NULL
2 Dental 0.75 2000 1/1/2019 NULL
That is, even when the ben plan is medical, I need to show the rate for Dental plan in the Rate column, or should I say, the rate column should display the result of following query:
SELECT Rate
FROM BenPlan
WHERE BenPlanName = 'Dental'
How can we do this?

Answer 1

Well, the following query returns your expected result. It always returns Rate of the Dental plan.
SELECT
EmployeeBenPlan.EmployeeId
,BenPlan.BenPlanName
,(
SELECT Rate
FROM BenPlan
WHERE BenPlanName = 'Dental'
) AS Rate
,BenPlan.EmployeeCost
,EmployeeBenPlan.EffectiveStart
,EmployeeBenPlan.EffectiveEnd
FROM
EmployeeBenPlan
INNER JOIN BenPlan ON BenPlan.BenPlanId = EmployeeBenPlan.BenPlanId
;
If the table BenPlan can have more than one row where BenPlanName = 'Dental', then you should somehow pick a single row. You can add TOP(1) with a suitable ORDER BY to the subquery.
SELECT TOP(1) Rate
FROM BenPlan
WHERE BenPlanName = 'Dental'
ORDER BY BenPlanId

Answer 2

You can use the following solution. This solution also works in case you are adding new records on BenPlan:
SELECT ebp.EmployeeId, bp.BenPlanName, bp.BenPlanRate AS Rate, bp.EmployeeCost, ebp.EffectiveStart, ebp.EffectiveEnd
FROM EmployeeBenPlan ebp INNER JOIN (
SELECT b1.BenPlanId, b1.BenPlanName, b1.EmployeeCost,
CASE WHEN b1.BenPlanName = 'Medical' THEN b2.BenPlanRate ELSE b1.BenPlanRate END AS BenPlanRate
FROM BenPlan b1 LEFT JOIN BenPlan b2 ON b1.BenPlanName = 'Medical' AND b2.BenPlanName = 'Dental'
) bp ON ebp.BenPlanId = bp.BenPlanId
ORDER BY ebp.EmployeeId, ebp.BenPlanId
demo on dbfiddle.uk

Answer 3

you can write this query
SELECT E.EmployeeId,B.BenPlanName,(SELECT TOP(1) Rate
FROM BenPlan
WHERE BenPlanName = 'Dental') AS Rate,
B.EmployeeCost,E.EffectiveStart,E.EffectiveEnd
FROM BenPlan B
INNER JOIN EmployeeBenPlan E ON B.BenPlanId = E.BenPlanId

Answer 4

You seem to want two joins to benplan, one just for "Dental" and one for the name of the actual plan:
select ebp.EmployeeId, bp.BenPlanName,
bpd.Rate, bp.EmployeeCost,
ebp.EffectiveStart, epb.EffectiveEnd
from employeebenplan ebp join
benplan bp
on ebp.BenPlanId = bp.BenPlanId join
benplan bpd
on bpd.BenPlanName = 'Dental'